I would say Pluto in the houses would show were we all have obsessive tendencies.
In 1st, may have an obsession with sex, and physical appearance, or just may have tons of physical pressure on them which they need to release, physically.
In 2nd, may obsess over having money, and obsess over possesions. This may show that a physical addiction may possess them, they are in a sense "owned" or slaves to the substance their addicted to, out of need to feel some pleasure of the senses. A slave to their senses, or sensuality, or very possessive, treat others like sex objects.
In 3rd, may have obssesive thoughts, compulsion to constantly write or speak, or close friends have addictions (which killed some of them in my case)
In 4th obsessed with privacy, will keeping everything secret, esp the addiction(or addiction may be rooted in the family). May be compulsive eater, where food is the drug they're addicted to.
In 5th, may show a gambling addiction, obsession with a sport, or addicted to the thrill of the chase in dating. And yes, the physical act of procreating, or having sex may be a very intense experience for them, and they may get addicted to it, or actively seek it alot, as stress relief, or for "fun".
In 6th may show a workaholic or health-nut, obsessed w/a productive daily routine, or an addiction which eats their daily life and healthy away. This is where the addiction may directly impact employment or ability to function in daily life. May work with the addicted or have to deal with them daily.
In 7th addiction to another in a controlling relationship,stalking, obsessed w/an enemy, or how others view them. Or maybe it shows partners who are addicted.
**In 8th may show a real sex addiction here, or obssessed with solving mysteries, getting to the bottom of things. Obsessed with psychologically probing others, may be an addiction to underworld activities
In 9th addiction to learning, obsession with far away lands, or obsessed and fixated with certain religious beliefs.
In 10th addiction to fame, obsession over famous people(Pluto in Cap now, so arent we all). Or famous people whose addictions are well-known, or people obsessed with their public image, reputation, or achieving success is like a compulsion.
In 11th addiction being common to your peer group, or obsession with a certain cause. Your social group, or network obsessed with the same things. A society under addictions.
In 12th may show a deep rooted addiction or obsession that originated from a past lifetime, or is of mysterious origin. Here, they have a real chance of getting swept up in Neptunes' currents of drugs/alcohol, as the 12th is also the house of one's own undoing..Being controlled by an archetypal force, or some otherworldly spirit...